The present invention relates generally to cameras having self contained interchangeable photographic objective lenses which are alternatively selectively positionable in alignment with the optical axis of the camera, and more particularly to an improved focus adjusting device for use in such cameras.
Cameras have heretofore been available and proposed which are provided with multiple photographic objective lenses, each having different focal lengths, and which are built into and self contained in the camera for selective use in photographing depending upon the desired field of view. For example, such a camera may be provided with a separate telephoto lens and a standard objective lens, or may be provided with a separate telephoto lens and a wide angle objective lens. The different lenses may be alternately and selectively aligned with the optical axis of the camera to produce desired photographic effects.
In prior cameras of this type, the alternate lenses have typically been carried on a mounting plate slidable in a direction at right angles to the optical axis of the camera so that movement of the mounting plate in a direction transverse to the optical axis will position one of the lenses in optical alignment with the optical axis. Another type of arrangement provides for a plurality of lenses on a mounting disc supported on a pivot arranged parallel to the optical axis. Rotation of the disc will cause displacement of the lenses about the pivot for selective alignment with the optical axis.
In such cameras, each of the individual objective lenses carry a driven member which is externally movable in order to effect focusing adjustment of each such lens. In order to effect external movement of such driven members, the camera is usually provided with a control member which engages only the driven member of the particular objective lens which is selectively positioned in optical alignment with the optical axis of the camera. Such a control member is typically manually operable in order to effect desired focusing adjustment of the selected lens. In the prior cameras, however, the engaging surface between the control member and the driven member, along which the control member and driven members engage each other, lies in a plane which is transverse to the direction of movement of the objective lenses when they are moved for interchangeable positioning. This arrangement prevents accurate focusing of the selected lens upon movement to the operative position.
Prior U.S. Pat. No. 4,119,983, filed on Nov. 12, 1976 and issued on Oct. 10, 1978 is typical of such cameras. In this patent, a camera is disclosed in which a pair of photographic objective lenses of different focal lengths are supported by a V-shaped lever. The V-shaped lever is pivotally mounted on a shaft arranged vertical with respect to the camera photographic optical axis. When the V-shaped lever is externally pivoted to a desired angular position, the photographic objective lenses are moved in an arcuate path about the shaft for interchangeable alignment along the optical axis of the camera. These interchangeable photographic objective lenses are each provided with a driven member which is movable and always urged or biased to return to a predetermined initial position. Each of the photographic objective lenses may be focused to any desired object distance by movement of its respective driven member. Also provided inside the camera is a control member linked with a manually operable distance setting member and constructed to engage the driven member of the photographic objective lens which is selectively positioned in alignment with the camera photographic optical path. Formed at a portion of the control member is a control surface which lies in a plane transverse to the direction of movement of the driven members of the photographic objective lenses when they are displaced to be interchanged. The control surface of the control member engages the driven member of the selected lens when it is moved into alignment with the camera optical axis. Therefore, when the distance setting member is externally moved, the driven member of the selected objective lens is moved from its initial position by the control surface of the control member so that focusing adjustment of the selected lens is effected.
As noted above, the control surface of the control member in the prior device lies in a plane which extends transverse to the direction of movement of the driven members of the objective lenses. Therefore, if the objective lens which is moved to the selected position deviates to any slight degree from the photographic optical path of the camera, the driven member of that selected lens will engage a portion of the control member other than the desired engaging portion of the control surface. This will prevent accurate focusing adjustment of the selected lens.
While it might be possible to overcome this disadvantage by strictly controlling the amount of movement of the photographic objective lens and its position on the optical path, it is extremely difficult to hold the objective lenses precisely in predetermined positions when they are interchanged. Accordingly, in cameras of the type where multiple lenses are selectively movable between operative and inoperative positions, the engaging relation between the driven member on each lens and the control member, which is linked to the distance member, will vary each time the objective lenses are interchanged, thereby seriously inhibiting accurate focusing adjustment.
Another possible means of overcoming the disadvantages in the prior arrangement would be to provide means for firmly and precisely holding the selected objective lens in a position along the optical path of the camera. However, such a holding means would result in additional forces to resist movement of the various objective lenses from the operative to the inoperative positions. This would therefore greatly limit the ability to quickly and smoothly change lenses.